1. Field of the Invention
The present invention relates to a magnetic memory apparatus and a method of manufacturing a magnetic memory apparatus, and, more particularly, to a nonvolatile-type magnetic memory apparatus and a method of manufacturing a magnetic memory apparatus which stores information by utilizing a change in a resistance value depending on spin orientation in a ferromagnetic material, which can be parallel or antiparallel.
2. Description of Related Art
With the rapid prevalence of information communication equipment, in particular, of personal compact equipment such as portable telephones, still more improved performance such as a higher circuit integration, faster speed, lower power consumption and the like is demanded for their memory devices, logic devices and the like for constituting the same. In particular, non-volatile memories are considered to be indispensable devices in the age of “ubiquitous”.
Even if a server and a network are interrupted by some failure due to, for example, power exhaustion or a trouble, the non-volatile memory can protect important personal information. Then, further improvement of the non-volatile memory so as to have a higher density and a larger capacity is becoming increasingly important as an alternative technology capable of replacing a hard disk and an optical disk which are essentially impossible to reduce the size thereof further because of the presence of movable parts therein.
Further, although the recent portable telephones are designed to be able to reduce power consumption as small as possible by holding the unnecessary circuit blocks thereof in a standby state, if a non-volatile memory that can function as a high speed network memory and as a large capacity storage memory is realized, wastes in power consumption as well as in memories can be eliminated. Still further, a so-called instant-on function capable of instant activation upon the power switch-on can be implemented if such a high speed, large-capacity non-volatile memory is realized.
As the non-volatile memories, there are cited a flash memory which uses semiconductors, a ferroelectric random access memory (FRAM) which uses ferroelectric materials, or the like. However, the flash memory has a drawback that its speed is low because of its write speed being a μ second order. Further, a large scale integration is difficult because of its complicated structure. Moreover, there is a disadvantage that its access time is slow, approximately in the order of 100 ns. On the other hand, as to the FRAM, some problems are indicated in that in order for it to completely replace the static random access memory (DRAM) or the dynamic random access memory (SRAM), its durability is low because of its rewritable frequency being 1012 to 1014 times. Further, a problem of difficulty in micro fabrication of the ferroelectric capacitor is also indicated.
A non-volatile memory drawing attention recently as having no such drawbacks described above is a magnetic memory referred to as a MRAM (magnetic random access memory) or a MR (magneto resistance) memory, which are drawing attention nowadays as a result of improvements in the characteristics of materials of recent tunneling magnetoresistance devices (hereinafter referred to as TMR: abbreviation of Tunnel Magnetic Resistance). (For example, see Wang et al., “Feasibility of Ultra-Dense Spin-tunneling Random Access Memory” IEEE Transaction on Magnetics 33 [6] (November 1997) p4498–4512)
The MRAM is easy to integrate because of its simple structure, and it is expected to have a large number of rewritable frequencies because of its storage of information being performed by rotation of magnetic moments. Further, as to its access time, a very high speed is expected, and, already, operability at 10 MHz has been reported (for example, see R. Scheuerlein et al, “TA7.2 A 10 ns Read and Write Non-Volatile Memory Array Using a Magnetic Tunnel Junction and FET Switch in each Cell” 2000 IEEE International Solid-State Circuits Conference Digest of Papers (February 2000) p128–129). At present, now a higher power output is obtainable due to a GMR effect, and it has been improved substantially.
Although the MRAM has such advantages that it is easy to realize a high speed and a large scale integration as described above, a write operation thereof is performed by a magnetic field that is generated when a current is passed through a bit line and a writing word line both provided adjacent to a TMR device. A reversing magnetic field necessary for reversal of a memory layer (storage layer) of the TMR device, although it depends on a material, is 1.58 kA/m to 15.8 kA/m (20 Oe to 200 Oe), and a current required at this time becomes several mA to several tens mA. This leads to increased power consumption, often resulting in a lowered service life, heating, and increased power consumption of the device which often become a demerit to semiconductors.
In order to address this problem regarding the increased power consumption, a structure capable of concentrating a magnetic field generated by the current by shielding the circumferences of a writing word line and a bit line (hereinafter referred to as a clad structure) has been proposed (see Japanese Patent Application Publication 2002-246566 (page 4, FIG. 6)).
FIG. 6 shows a schematic view in perspective of a part of a simplified MRAM using the clad structure formed with a magnetic material layer. As shown in FIG. 6, a circumference of a word line 11 is surrounded by a first magnetic material layer 16, except for the surface thereof facing a magnetoresistance-type memory device (for example, TMR device) 13, so as to concentrate a magnetic flux into the memory device 13. Likewise, a circumference of a bit line 12 is surrounded by a second magnetic material layer 17, except for the surface thereof facing the memory device 13, so as to concentrate a magnetic flux thereof into the memory device 13.